Toothed wheels and transmission

Abstract

A pair of toothed wheels that mesh with each other includes a plateau portion. The surface of the plateau portion is a plateau-structure surface formed on each tooth face of each of the pair of the toothed wheels, with peak portions of convexities, out of a plurality of concavities and the convexities provided on the each tooth face, being flat. A reduced valley depth Rvk of the plateau portion of one of the pair of the toothed wheels as defined in JISB0671-2 is greater than the reduced valley depth Rvk of the plateau portion of the other of the pair of the toothed wheels. The area occupied by the concavities in the plateau portion of the one of the toothed wheels is larger than the area occupied by the concavities in the plateau portion of the other toothed wheel.

The invention claimed is: 
     
       1. A pair of toothed wheels that mesh with each other, comprising:
 each tooth face of each of the pair of the toothed wheels including a plateau portion, a surface of the plateau portion being a plateau-structure surface, the plateau-structure surface having a plurality of concavities and a plurality of convexities, and peak portions of the plurality of convexities being flat, wherein 
 a reduced valley depth of the plurality of concavities of the plateau portion of one of the pair of the toothed wheels is greater than a reduced valley depth of the plurality of concavities of the plateau portion of the other of the pair of the toothed wheels, and 
 an area occupied by the plurality of concavities in the plateau portion of the one of the toothed wheels is larger than an area occupied by the plurality of concavities in the plateau portion of the other toothed wheel. 
 
     
     
       2. The toothed wheels according to  claim 1 , wherein reduced peak heights of both the plateau portion of the one of the toothed wheels and the plateau portion of the other toothed wheel are smaller than 1.0 μm. 
     
     
       3. The toothed wheels according to  claim 1 , wherein a hardness of teeth of the one of the toothed wheels is equal to a hardness of teeth of the other toothed wheel. 
     
     
       4. The toothed wheels according to  claim 1 , wherein the area occupied by the concavities in the plateau portion is an area other than the area of the peak portions of the plateau portion. 
     
     
       5. A transmission comprising:
 an input shaft; 
 an output shaft; and 
 a plurality of gear pairs that are interposed between the input shaft and the output shaft and are different in speed ratio from each other, wherein 
 the input shaft is provided with one of toothed wheels of each of the plurality of the gear pairs, 
 the output shaft is provided with the other toothed wheel of each of the plurality of the gear pairs such that the other toothed wheel meshes with the one toothed wheel, 
 a changeover in speed ratio is made by selectively achieving transmission of rotation by one of the plurality of the gear pairs, and 
 the toothed wheels according to  claim 1  are provided as at least one of the plurality of the gear pairs. 
 
     
     
       6. The transmission according to  claim 5 , wherein the plurality of the gear pairs include a gear pair at an intermediate shift speed, a gear pair at a low shift speed which is higher in speed ratio than the gear pair at the intermediate shift, speed, and a gear pair at a high shift speed which is lower in speed ratio than the gear pair at the intermediate shift speed, and
 the toothed wheels are provided as the gear pair at the intermediate shift speed. 
 
     
     
       7. The transmission according to  claim 6 , wherein the plateau portion includes a first plateau portion and a second plateau portion,
 the first plateau portion is provided on each tooth face of each toothed wheel of the gear pair at the low shift speed, 
 the second plateau portion is provided on each tooth face of each toothed wheel of the gear pair at the high shift speed, 
 the reduced valley depth of the first plateau portion is greater than a predetermined value, and an area occupied by concavities in the first plateau portion is larger than an area occupied by the peak portions of the convexities on the first plateau portion, and 
 the reduced valley depth of the second plateau portion is smaller than the predetermined value, and an area occupied by the peak portions of the convexities on the second plateau portion is larger than an area occupied by the concavities in the second plateau portion. 
 
     
     
       8. The toothed wheels according to  claim 1 , wherein the pair of toothed wheels rotate about separate shafts.